Surface Structures and Dielectric Properties of Yttrium-doped Barium Strontium Titanate Films by Improved Sol-Gel method

Normal Sol-Gel method was improved by adding polyvinyl pyrrolidone to sol and forming seed layer on Pt electrode. Undoped and Yttrium (Y)-doped Ba0.6Sr0.4TiO3 (BST) films were prepared on Pt/Ti/SiO2/Si by the improved Sol-Get method. The surface structures and dielectric tunable properties of the as-prepared BST films were investigated. X-ray photoelectron spectrum (XPS) shows that Ba3d, Sr3d, Ti2p or O1s on the surfaces of BsT films displays two or three chemical states, and. these chemical states correspond to perovskited structure and non-perovskited structure. Y doping has significant effect oil the chemical states of Ba3d, Sr3d and O1s except those of Ti2p, and makes the contents of Ba, Sr and O atoms in non-perovskited structure decrease from 41% to 26%, from 33% to 29% and from 51% to 40%, respectively, thus results in large decrease of non-perovskited structure. Meanwhile, scanning electron microscope (SEM) and atomic force microscope (AFM) demonstrate that Y-doped BST films show prominent improvement in morphologies with smooth and compact surface with no crack or shrinkage cavity. Such morphologies visibly decrease the adsorption of gases and hydrocarbon contaminations and their diffusion passes, which is the probable reason for non-perovskited structure to be formed. Also, voltage-capacitance curves obtained at 40V and 100kHz illustrate that Y-doped BST films exhibit improved dielectric tunable properties with tunability of more than 43%, dielectric loss of 0.0216 and merit factor value of 20. Additionally, the improved mechanism of Y doping is discussed.